Conditional task with pg-promise

问题:

I am trying to simply read a value from a table and based on the return value call for additional queries and return the combined results.

let's take a simple example: table Users has id, name and emailid and let's say if emailid is not null we want to call the email table and return a results like { id:[id], name:[name], email:[email]}.

回答1:

Using the latest syntax supported by pg-promise:

db.task(t => {
    return t.map('SELECT * FROM Users', [], user => {
        return user.emailid ?
            t.one('SELECT * FROM Emails WHERE id = $1', user.emailid, e=> {
                user.email = e.email;
                return user;
            }) : user;
    }).then(t.batch);
})
    .then(data => {
        // success
    })
    .catch(error => {
        // error
    });

See the API: Database.map, Database.one.

See also a related question: Get a parents + children tree with pg-promise.

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NOTE: A better approach would use a single query with INNER JOIN.